This invention relates to door lock mechanisms, and particularly to a drive assembly for connecting a door handle shell or the like to a handle body that is coupled to a door latching system and adapted to disconnect under conditions of excessive torque to prevent the transmission to the door lock mechanism of excessive torque applied to the door handle. As used herein, the term "handle" is intended to include levers, knobs, and the like.
Door locks are subject to attack by the exertion of high torque on the handle sufficient to damage or override the lock mechanism and thus to jeopardize the security of the lock. Levered handles are particularly susceptible to the application of such excssive torque, since a strong person may be able to twist the lever handle manually with sufficient force to apply such high torque. Lever handles are also liable to attack by the application of force with the use of a tool applied to the projecting lever of the handle. Nevertheless, levered handles are desirable and in some cases mandatory to facilitate operation of door locks by handicapped or other persons who are not able to grip and turn a round knob.
Door handles having lock drive assemblies adapted to engage and rotate a bolt-retracting sleeve under normal operating torque but to release under excessive torque permitting the door handle to rotate with respect to the bolt-retracting sleeve are known. Conventional torque-releasable drive assemblies typically provide a releasable connecting directly between the door handle and the bolt-retracting sleeve itself. For example, a frangible drive coupling a knob to a knob sleeve and having drive lugs configured to shear in the shear region between the knob and sleeve under excess torque is disclosed in U.S. Pat. No. 4,550,581 to Best et al. In addition, U.S. Pat. No. 4,394,821 to Best et al. discloses a positive driver coupling a knob to a knob sleeve that is spring-biased to its driving position and cammed under excessive torque to a retracted position to release the normal drive connection between the knob and the knob sleeve.
One object of the present invention is to provide a torque-releasable drive assembly that is spring-biased to establish a normal driving connection and configured to ensure that application of torque to the handle in excess of a predetermined amount consistently acts to release the normal driving connection.
Another object of the present invention is to provide a torque-releasable handle assembly having a spring-biased camming driver that is easily resettable to a normal operating position following each application of excessive torque to the handle.
In accordance with the present invention, a torque-releasable door handle assembly is provided for normally rotating a bolt-retracting sleeve to operate a door latching system. The door handle assembly includes a body for coupling to the bolt-retracting sleeve and a handle shell mounted on the body for rotational movement thereabout. Drive means is provided for yieldably connecting the body and handle shell to establish a normal driving connection so that the body is rotated normally to rotate the bolt-retracting sleeve and operate the door latching system in response to rotation of the handle shell. The drive means is configured to release the normal driving connection between the body and the handle shell in response to application of a rotation-inducing torque to the handle shell in excess of a predetermined amount.
In preferred embodiments, the drive means includes a matched pair of mateable drive rings positioned in a space between an exterior surface of the body and an interior surface of the handle shell. A female drive ring includes a plurality of lug-receiving recesses. The female drive ring is positioned in the space to present its lug-receiving recesses in an axially inward door-facing direction and is coupled to the body for rotation therewith. A companion male drive ring includes a plurality of drive lugs shaped to engage the lug-receiving recesses of the female drive ring. The male drive ring is positioned in the space to present its drive lugs toward the female drive ring and is coupled to the handle shell for rotation therewith. In addition, the male drive ring is reciprocable in the space between an inactive position in spaced relation to the female drive ring and a torque-transmitting position in engagement with the female drive ring.
The drive means further includes spring means for yieldably biasing the male drive ring toward its torque-transmitting position to establish a normal driving connection between the body and the handle. The male drive ring is moved against the spring means toward its inactive position to release the normal driving connection in response to application of a rotation-inducing torque to the handle shell in excess of a predetermined amount.
In one embodiment of the present invention, the male drive ring is coupled to a radially inwardly-extending annular lip of the handle shell and the spring means acts directly between the male drive ring and the annular lip. In another embodiment, the male drive ring is a part of a subassembly coupled to an interior surface of the handle shell and the spring means is resiliently trapped within the subassembly between the male drive ring and an opposite end causing the opposite end to abut a radially inwardly-extending lip of the handle shell in biased relation.
One feature of the present invention is the provision of a handle assembly having torque-releasable drive means for yieldably interconnecting adjacent handle members to establish a normal driving connection that is releasable under excess torque to protect its companion door-latching system from damage during an attack on the security of the lock or other improper usage. This feature is positioned in a radially-outer location in the handle assembly itself and advantageously replaces conventional torque-releasable drivers that are often situated in interior regions of the door lock mechanism and interconnect a knob and a bolt-retracting knob sleeve. The novel door handle assembly of the present invention is more easily assembled, lubricated, and otherwise serviced than conventional torque-releasable drivers. In addition, provision of a spring-biased driver makes it unnecessary to disassemble and replace conventional frangible drivers that are broken during an attack following each instance of breakage.
Another feature of the present invention is the provision of a pair of separate drive rings in the handle assembly that are mateable to establish the normal driving connection. These companion drive rings advantageously provide broad mateable engagement surfaces that spread the biasing load generated by the spring means over a large contact area to lengthen the operating life of the novel torque-releasable drive means in comparison to known torque-releasable drive means having a small engagement region defined, for example, by one or two small lugs in engagement with a bolt-retracting sleeve or the like.
Another feature of the present invention is the provision of spring means for yieldably biasing a reciprocable drive ring toward a nonreciprocable drive ring to establish the normal driving connection. Advantageously, the novel spring means can be oriented to act along a longitudinal axis established by the handle body and shell to apply a substantially uniform biasing pressure to the reciprocable drive ring so that the normal driving connection is consistently released in response to application of a rotation-inducing torque to the handle shell in excess of a selected torque magnitude. This feature advantageously improves the camming operation of the spring-biased drive rings in that the threshold torque which must be applied to the handle shell to cam the reciprocable drive ring to a disengaged position is substantially constant.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.